R-2721, S-2-(3-aminopropylamino) ethylphosphorothioate, is a sulfydryl radioprotective compound with the ability to selectively protect normal tissue against radiation damage and leave malignant tissue unprotected. Recent studies by this investigator show that 35S-labeled WR-2721 has viriable absorption within normal tissues of the mouse and essentially no absorption in an in situ tumor model. Radioprotection in some normal tissues which show a high drug concentration has been established. Other such organs have not been studied. This investigation is designed to evaluate acute and chronic radioprotection in liver, salivary gland, and vasculoconnective tissue and to determine if a variety of animal tumors are indeed poorly protected. If additional information continues to support the fact that normal tissue is preferentially radioprotected by R-2721, the clinical usefulness of this drug appears clear.